Abstract
Dairy cows near Princeton, N. J., have shown an unusually high incidence of bloody thickened milk during the spring, summer and fall of 1946. The majority of cases occurred in the latter part of May and in June and animals in all stages of lactation were affected. Many specimens of abnormal milk contained flakes composed of polynuclear and mononuclear cells. Affected animals frequently showed temperatures exceeding 40°C but otherwise appeared normal and continued to eat as usual. In most cases all visible signs disappeared after 2 to 4 days. These facts suggested an infectious nature and investigations were made in an attempt to procure the etiological agent.
Guinea pigs weighing 200 to 300 g and kept under constant conditions of temperature (70°F) and humidity (60%) were inoculated intraperitoneally with either 1 or 5 cc of milk freshly drawn from naturally infected cows. From each of 3 milk samples furnished by different cows an agent was established in guinea pigs that caused temperature elevations exceeding 40°C beginning 4 to 7 days after inoculation and lasting for 3 days. Other than fever no definite signs of illness were noted, and all animals survived unless killed for further study. Animals killed during the febrile period showed hemorrhages in the lungs, focal necrosis of the liver and slightly enlarged mesenteric lymph nodes. These findings remained constant through 20 serial passages in guinea pigs maintained by blood transfers. Following recovery animals given a second inoculation with the same strain showed no response and in cross inoculations between the 3 strains it was found that each immunized against the others. Therefore presence of the agent was determined by a typical thermal response in guinea pigs, followed by subsequent immunity to test inoculation with a reference strain.
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